leds: leds-lp55xx: Use correct address for memory programming

Memory programming doesn't work for devices without page support.
For example, LP5562 has 3 engines but doesn't support pages,
the start address is changed depending on engine number.
According to datasheet [1], the PROG MEM register addresses for each
engine are as follows:

Engine 1: 0x10
Engine 2: 0x30
Engine 3: 0x50

However, the current implementation incorrectly calculates the address
of PROG MEM register using the engine index starting from 1:

prog_mem_base = 0x10
LP55xx_BYTES_PER_PAGE = 0x20

Engine 1: 0x10 + 0x20 * 1 = 0x30
Engine 2: 0x10 + 0x20 * 2 = 0x50
Engine 3: 0x10 + 0x20 * 3 = 0x70

This results in writing to the wrong engine memory, causing pattern
programming to fail.

To correct it, the engine index should be decreased:
Engine 1: 0x10 + 0x20 * 0 = 0x10
Engine 2: 0x10 + 0x20 * 1 = 0x30
Engine 3: 0x10 + 0x20 * 2 = 0x50

1 - https://www.ti.com/lit/ds/symlink/lp5562.pdf

Fixes: 31379a57cf2f ("leds: leds-lp55xx: Generalize update_program_memory function")
Signed-off-by: Andrei Lalaev <andrei.lalaev@anton-paar.com>
Link: https://lore.kernel.org/r/20250820-lp5562-prog-mem-address-v1-1-8569647fa71d@anton-paar.com
Signed-off-by: Lee Jones <lee@kernel.org>